Effects of Mid-Latitude Oceanic Fronts on the Middle Atmosphere Through Upward Propagating Atmospheric Waves

The impact of mid-latitude oceanic frontal zones with sharp meridional sea-surface temperature (SST) gradients on the middle atmosphere circulation during austral winter is investigated by comparing two idealized experiments with a high-top gravity wave (GW) permitting general circulation model. Control run is performed with realistic frontal SST gradients, which are artificially smoothed in no-front run. The control run simulates active baroclinic waves and GW generation around the mid-latitude SST front, with GWs propagating into the stratosphere and mesosphere. In the no-front run, by contrast, baroclinic-wave activity is significantly suppressed, and GWs with smaller amplitude are excited and then dissipated at higher altitudes in the mesosphere. Westward wave forcing in the winter hemisphere was more pronounced in the control run up to similar to 0.03 hPa, resulting in a more realistic reproduction of the middle atmospheric polar vortex. The results demonstrate the importance of realistic mid-latitude ocean conditions for simulating the middle atmosphere circulation. Plain Language Summary The impact of the mid-latitude oceanic fronts characterized by sharp sea-surface temperature (SST) gradients is investigated using a global gravity-wave permitting atmospheric model that represents the troposphere, stratosphere and mesosphere. Two idealized experiments were conducted with different SST profiles. Control run features a realistic SST profile characterized by frontal SST gradients in mid-latitudes, while they are smoothed out artificially in the "no-front" run. In winter the no-front run simulates significantly suppressed generation of synoptic-scale cyclones and anticyclones, which results in reduced upward propagation of higher-frequency gravity waves into the stratosphere, exerting marked impact on the large-scale circulation extending as high as the mesopause. Notably higher gravity wave activity in the control run leads to a weaker, and more realistic wintertime polar vortex in the stratosphere and mesosphere. This study emphasizes the potential influence of mid-latitude oceanic conditions on the atmospheric circulation, not only in the troposphere but also throughout the stratosphere and mesosphere.